Optimal mechanical force-velocity profile for sprint acceleration performance

Effects of vertical and horizontal plyometric training on jump performances and sprint force-velocity profile in young elite soccer players

PURPOSE

During a soccer match, horizontal acceleration ability during short sprints is determinant for performance. Development of sprint force and velocity qualites have been reported after plyometric training. However, orientation of plyometric training exercises can influence the functional performance. The purpose of this study was to compare the horizontal and vertical orientation of plyometric training on explosiveness performances and sprint force-velocity profile in young soccer players.

METHODS

Twenty-eight soccer players were recruited and divided in two groups: vertical (VG, n = 14) and horizontal (HG, n = 14) groups. Tests including jumps and sprint performances were conducted before and after the 8 week training period. Sprint force-velocity profile (FVP) was evaluated during a 30 m sprint test.

RESULTS

The results demonstrated significant improvements in both VG and HG for jump performances (from + 4.9% to + 9.0%), sprint times (from -5.5% to -8.7%) and FVP parameters. Higher relative changes for the HG than for the VG were observed in 5 m and 15 m sprint times, horizontal jump lengths, and also in FVP parameters, especially improvements in maximal power (VG: + 16.4% vs. HG: + 28.1%) and in the decrease rate of horizontal orientation of force with increasing speed (HG: + 22.9%) during the 30 m sprint.

CONCLUSIONS

Both horizontal and vertical plyometric training can be either used in young soccer players to improve vertical and horizontal performances in jump and sprint. However, horizontal plyometric training may result in a greater improvement in horizontal ballistic actions while similarly developing vertical jump qualities compared to vertical plyometric training in young soccer players.

The relationship between off-ice testing and on-ice performance in male youth Ice hockey players

Introduction

Ice hockey demands a unique blend of physical fitness and skill, necessitating a comprehensive understanding of the factors influencing on-ice performance. The present study was designed to examine the relationship between off-ice and on-ice performance measures in male, youth, ice hockey players.

Methods

Eleven minor hockey players (Age = 9.8 ± 1.1 years) participated in two testing days: (1) off-ice and (2) on-ice assessments. Off-ice assessments included maximal aerobic power, anaerobic fitness, muscular strength (handgrip and single leg squat), muscular endurance (curl-ups and push-ups), muscular power (standing long jump and vertical jump), and 30 m sprinting speed and acceleration. On-ice testing included a 15.2 m maximum speed test, a 6.1 m acceleration test with a continuation into a 47.9 m top speed test, an agility cornering S turn test, and a shot velocity test.

Results

Twenty-four out of 33 off-ice variables were significantly correlated with at least one of the 11 on-ice performance variables. From those 24, 10 were included as predictors for at least one of the on-ice performance variables. Each model was composed of either one or two predictors, where the most common predictors were 30 m Run - Split (6.1 m) Sprint time and 30 m Run - Total (30 m) Sprint Max speed (included in four out of 11 models each). The prediction formulas R2 and coefficient of variation ranged from 0.63% to 0.96% and 1.2% to 15.3%, respectively.

Discussion

Diverse off-ice measures of aerobic fitness, anaerobic power, muscular strength, power, and endurance, and sprinting speed, acceleration, and agility are predictive of on-ice performance. The insights gained from this study contribute to the refinement of assessment protocols, fostering a comprehensive approach to optimizing player performance and potential. Understanding the connection between objective off-ice testing and on-ice performance can support tailored training programs and player development in male youth ice hockey.

Testing in Intermittent Sports-Importance for Training and Performance Optimization in Adult Athletes

ABSTRACT

Performance in intermittent sports relies on the interplay between multiple physiological systems determining the capacity to perform short explosive efforts as well as repeated intense actions with limited recovery over the course of an entire game. Testing should reflect these demands to allow for sport- and position-specific capacity analyses that eventually may translate into optimized training and improved performance. This may include individual load management and optimized training prescription, intensity targeting for specific positions or individual athletes, as well as benchmarking for monitoring of training progression and enhanced engagement of athletes. This review provides an overview of available tests in different exercise domains identified as relevant (from assessment of single explosive actions to intermittent endurance capacity), forming the basis for recommendations on how to compose a comprehensive yet feasible test battery that may be integrated into the seasonal competition and training plan. The test procedures should cover the performance spectrum of relevance for the individual athlete-also in team sports to account for positional differences. We emphasize the benefits of sport-specific tests, highlight parameters of importance for test standardization, and discuss how the applied test battery may be supplemented with secondary tests directed toward specific energy systems to allow for more in-depth analyses when required (e.g., in terms of an underperforming athlete). The synergy between testing and tracking of match performance (utilizing time-motion or global positioning systems) is highlighted, and although tracking cannot substitute for testing, combining the tools may provide a comprehensive overview of the physiological demands and performance during competition contextualized to the athletes' maximal exercise capacity.

Using Inertial Measurement Units to Examine Selected Joint Kinematics in a Road Cycling Sprint: A Series of Single Cases

Sprinting plays a significant role in determining the results of road cycling races worldwide. However, currently, there is a lack of systematic research into the kinematics of sprint cycling, especially in an outdoor, environmentally valid setting. This study aimed to describe selected joint kinematics during a cycling sprint outdoors. Three participants were recorded sprinting over 60 meters in both standing and seated sprinting positions on an outdoor course with a baseline condition of seated cycling at 20 km/h. The participants were recorded using array-based inertial measurement units to collect joint excursions of the upper and lower limbs including the trunk. A high-rate GPS unit was used to record velocity during each recorded condition. Kinematic data were analyzed in a similar fashion to running gait, where multiple pedal strokes were identified, delineated, and averaged to form a representative (average ± SD) waveform. Participants maintained stable kinematics in most joints studied during the baseline condition, but variations in ranges of movement were recorded during seated and standing sprinting. Discernable patterns started to emerge for several kinematic profiles during standing sprinting. Alternate sprinting strategies emerged between participants and bilateral asymmetries were also recorded in the individuals tested. This approach to studying road cycling holds substantial potential for researchers wishing to explore this sport.

Using a simple model to systematically examine the influence of force-velocity profile and power on vertical jump performance with different constraints

Power, and recently force-velocity (F-V) profiling, are well-researched and oft cited critical components for sports performance but both are still debated; some would say misused. A neat, applied formulation of power and linear F-V in the literature is practically useful but there is a dearth of fundamental explanations of how power and F-V interact with human and environmental constraints. To systematically explore the interactions of a linear F-V profile, peak power, gravity, mass, range of motion (ROM), and initial activation conditions, a forward dynamics point mass model of vertical jumping was parameterised from an athlete. With no constraints and for a given peak power, F-V favouring higher velocity performed better, but were impacted more under real-world conditions of gravity and finite ROM meaning the better F-V was dependent on constraints. Increasing peak power invariably increased jump height but improvement was dependent on the initial F-V and if it was altered by changing maximal force or velocity. When mass was changed along with power and F-V there was a non-linear interaction and jump improvement could be almost as large for a F-V change as an increase in power. An ideal F-V profile cannot be identified without knowledge of mass and ROM.

The Force-Velocity Profiling Concept for Sprint Running Is a Dead End

PURPOSE

In this commentary, I present arguments against the use of the force-velocity profiling concept in design and adaptations of training programs targeting sprinting. The purpose of this commentary is to make sports practitioners more aware of the rationale behind the concept and explain why it does not work.

RATIONALE

Force-velocity profiling is a mathematical way to present the velocity development during sprint behavior. Some details of this behavior may be accentuated by transforming it to other variables, but it does not add any new information about sprint performance. Thus, contrary to what is often claimed, the force-velocity profile does not represent maximal capacities (ability of force and velocity generation) of the athlete. It is claimed that through force-velocity profiling one may identify the optimal ratio of force and velocity capacities. Furthermore, proponents of the force-velocity profiling concept suggest that through directed training force and velocity capacities can be altered (inversely dependent) to obtain this optimal ratio, without changing the capacity to express power. Fundamentally, this idea is unfounded and implausible.

CONCLUSION

At best, force-velocity profiling may be able to identify between-athletes differences. However, these can be more easily deduced directly from performance time traces.

Exploring associations between sprinting mechanical capabilities, anaerobic capacity, and repeated-sprint ability of adolescent ice hockey players

Introduction

Sprinting ability and anaerobic capacities are the determinant variables of the performance of ice hockey players. Recent research in sprinting showed the existence of distinct force-velocity (F-V) profiles, but the link between these profiles and anaerobic capacities remains unclear. This study explores the associations between F-V variables and anaerobic capacities among cohorts of highly trained adolescent ice hockey players.

Methods

Data from 36 men (age, 15.1 ± 0.2 years) and 34 women (age, 16.5 ± 0.7 years) were collected during off-season camps. All athletes completed a 30-m sprint test, a Wingate anaerobic test (WAnT), and a repeated-sprint anaerobic (RSA) test. F-V variables were calculated from the 30-m sprint test. Partial Pearson correlation coefficients for pooled data and Pearson correlation coefficients for individual male and female datasets were calculated.

Results

Among the F-V variables, maximal theoretical velocity and power were moderately to largely associated with WAnT and RSA performance (|r| = 0.30-0.70). Maximal theoretical force was moderately associated with the RSA (r = -0.32 to -0.33).

Discussion

The results indicate the importance for highly trained adolescent players to be able to apply force at high velocities to maximize anaerobic capacities. Important differences between male and female players suggest training priorities may differ according to sex.

Jump and sprint force velocity profile of young soccer players differ according to playing position

Our study aimed to compare explosive performance and underlying mechanical determinants explored through F-V profiles in jumping and sprinting among young soccer players based on their playing position. Ninety elite soccer players were categorized into the following positions: goalkeepers, central defenders, wide defenders, central midfielders, wide midfielders, and forwards. Two testing sessions were conducted to measure the 30-metre sprint time (T30) using an over-ground sprint test and jump height (Hmax) through the SJ test. Results demonstrated performance variations among positions. In sprinting, forwards showed greater T30 (4.5 ± 0.14 s) compared to other positions, with goalkeepers exhibiting the lowest T30 (4.86 ± 0.18 s). Forwards also displayed higher maximal theoretical velocity (8.8 ± 0.4 m.s-1) and power output (Pmax) (19.4 ± 2.6 W.kg-1) than other positions, while goalkeepers had the lowest Pmax (16.5 ± 2 W.kg-1). In jumping, forwards (33.2 ± 3.9 cm) and wide-midfielders (33.6 ± 3.8 cm) achieved higher Hmax compared to goalkeepers (29.2 ± 5 cm) and central-midfielders (29.2 ± 3.8 cm). Wide-midfielders (28.5 ± 4.8 W.kg-1) and forwards (27.1 ± 4.3 W.kg-1) surpassed goalkeepers (23 ± 2.8 W.kg-1) and central-midfielders (25.1 ± 3.8 W.kg-1) in Pmax. Our findings reveal substantial position-related disparities in F-V profiles among elite young soccer players, in sprinting and jumping emphasizing the need for position-specific training programmes to optimize player development and on-field performance from an early age.

The 2-Point Method: Theoretical Basis, Methodological Considerations, Experimental Support, and Its Application Under Field Conditions

The "2-point method," originally referred to as the "2-load method," was proposed in 2016 by Prof Slobodan Jaric to characterize the maximal mechanical capacities of the muscles to produce force, velocity, and power. Two years later, in 2018, Prof Jaric and I summarized in a review article the scientific evidence showing that the 2-point method, compared with the multiple-point method, is capable of providing the outcomes of the force-velocity (F-V) and load-velocity (L-V) relationships with similar reliability and high concurrent validity. However, a major gap of our review was that, until 2018, the feasibility of the 2-point method had only been explored through testing procedures based on multiple (more than 2) loads. This is problematic because (1) it has misled users into thinking that implementing the 2-point method inevitably requires testing more than 2 conditions and (2) obtaining the data from the same test could have artificially inflated the concurrent validity of the 2-point method. To overcome these limitations, subsequent studies have implemented in separate sessions the 2-point method under field conditions (only 2 different loads applied in the testing protocol) and the standard multiple-point method. These studies consistently demonstrate that while the outcomes of the 2-point method exhibit comparable reliability, they tend to have slightly higher magnitudes compared with the standard multiple-point method. This review article emphasizes the practical aspects that should be considered when applying the 2-point method under field conditions to obtain the main outcomes of the F-V and L-V relationships.

Monitoring Changes in Lower-Limb Strength and Power in Elite Athletes With the Countermovement-Jump and Keiser Leg-Press Tests

PURPOSE

To determine the utility of countermovement-jump and Keiser leg-press tests for tracking changes in elite athletes of different sports.

METHODS

Elite athletes of the Norwegian Olympic Federation (126 individuals from 18 sports) performed countermovement-jump and Keiser tests on 2 to 11 occasions between 2014 and 2021. Separate analyses were performed for male and female alpine skiing, male and female handball, male ice hockey, and males and females of other sports. Means and standard deviations of consecutive change scores were combined with short-term error of measurement (3.7%-7.0%) and smallest important changes (2.0%-3.6%, defined by standardization) to determine the proportions of athletes who experienced decisive changes in 2 senses: first, the athlete did not get substantially worse or better (>90% chance of either), and second, the athlete did get substantially worse or better (>90% chance of either).

RESULTS

Averaged over sports, Keiser peak power and relative peak power had the highest proportions of decisive changes in the first (60% and 55%) and second senses (25% and 28%). The velocity intercept of the force-velocity relationship had the lowest proportions in the first and second senses (29% and 11%), while jump height, Keiser mean power, relative mean power, the force intercept, and the slope of the force-velocity relationship had similar proportions (40%-53% and 15%-21%).

CONCLUSIONS

With the possible exception of the Keiser test velocity intercept, the proportions of observed decisive changes in elite athletes using Keiser measures and countermovement-jump height between tests appear adequate for the measures to be useful for routine monitoring.

In-situ acceleration-speed profile of an elite soccer academy: A cross-sectional study

Speed is an essential skill in sports performance and an important performance metric in talent identification. This study aims to evaluate and compare the sprint acceleration characteristics across different age groups in an elite soccer academy. A total of 141 elite academy soccer players were recruited to participate in the study, and they were assigned to their respective competitive age groups, ranging from under-14 to the B-team. An individual in-situ acceleration-speed (A-S) profile was assessed and derived from Global Position System (GPS) speed-acceleration raw data, from 10 consecutive football sessions, in the beginning of the season. The results showed that under-14 players exhibited significantly lower theoretical maximum speed (S0) (η p 2  = 0.215, p < 0.01) when compared with all other age groups. However, no differences were found between maximum theoretical acceleration (A0) and A-S slope between age groups. The results suggest that sprint mechanical profiles of young soccer athletes remain stable throughout their athletic development. Nevertheless, younger athletes have less capacity to apply horizontal force at higher speeds (S0).

Mechanical Determinants of Sprinting and Change of Direction in Elite Female Field Hockey Players

Profile determination in field hockey is critical to determining athletes' physical strengths and weaknesses, and is key in planning, programming, and monitoring training. This study pursued two primary objectives: (i) to provide descriptive data on sprinting, deceleration, and change of direction (COD) abilities and (ii) to elucidate the mechanical variables that influence sprint and COD performance in elite female field hockey players. Using radar and time-gate technology, we assessed performance and mechanical data from 30 m sprinting, deceleration, and COD tests for 26 elite female hockey players. A machine learning approach identified mechanical variables related to sprint and COD performance. Our findings offer a framework for athlete categorization and the design of performance-enhancing training strategies at the international level. Two pivotal mechanical variables-relative maximum horizontal force (F0) and maximum velocity (Vmax)-predominantly influence the times across all tested distances. However, the force-velocity profile (FVP) and horizontal deceleration do not influence the variance in the COD test outcomes. These insights can guide the design, adjustment, and monitoring of training programs, assisting coaches in decision making to optimize performance and mitigate injury risks for female hockey players.

Opposition Skill Efficiency During Professional Rugby Union Official Games Is Related to Horizontal Force-Production Capacities in Sprinting

PURPOSE

This study aimed to determine relationships between parameters of force-production capacity in sprinting and opposition skill efficiency in rugby union games according to position.

METHODS

The sprint force-velocity profile of 33 professional rugby union players divided into 2 subgroups (forwards and backs) was measured on a 30-m sprint. Skill efficiencies (in percentage) of offensive duels, tackles, and rucks were assessed using objective criteria during 12 consecutive competitive games. Pearson correlation was used to determine the relationships between parameters of horizontal force-production capacity in sprinting (maximum propulsive power, theoretical maximum force [F0], theoretical maximum velocity, maximum ratio of horizontal force [RFmax], and rate of decrease of this ratio of forces with increasing velocity) and skill efficiencies. Two multiple linear regression models were used to observe whether skill efficiencies could depend on determinants of horizontal force application in low- or high-velocity conditions. A first model including F0 and theoretical maximum velocity was used as a macroscopic analysis, while a second model including RFmax and rate of decrease of this ratio of forces with increasing velocity was used as microscopic analysis to determine the most significant determinants of skill efficiency.

RESULTS

All skill efficiencies were strongly correlated with maximum propulsive power in forwards and backs. In forwards, F0 and RFmax were the key predictors of dueling, rucking, and tackling efficiency. In backs, F0 was the main predictor of dueling and rucking efficiency, whereas RFmax was the key predictor of dueling and tackling efficiency. F0 and theoretical maximum velocity equivalently contributed to tackling performance.

CONCLUSIONS

In rugby union forward and back players, skill efficiency is correlated with maximum propulsive power and may be more explained by horizontal force-production capacity and mechanical effectiveness at lower velocities than at higher velocities.

Wheelchair Rugby Sprint Force-Velocity Modeling Using Inertial Measurement Units and Sport Specific Parameters: A Proof of Concept

BACKGROUND

Para-sports such as wheelchair rugby have seen increased use of inertial measurement units (IMU) to measure wheelchair mobility. The accessibility and accuracy of IMUs have enabled the quantification of many wheelchair metrics and the ability to further advance analyses such as force-velocity (FV) profiling. However, the FV modeling approach has not been refined to include wheelchair specific parameters.

PURPOSE

The purpose of this study was to compare wheelchair rugby sprint FV profiles, developed from a wheel-mounted IMU, using current mono-exponential modeling techniques against a dynamic resistive force model with wheelchair specific resistance coefficients.

METHODS

Eighteen athletes from a national wheelchair rugby program performed 2 × 45 m all-out sprints on an indoor hardwood court surface.

RESULTS

Velocity modelling displayed high agreeability, with an average RMSE of 0.235 ± 0.07 m/s-1 and r2 of 0.946 ± 0.02. Further, the wheelchair specific resistive force model resulted in greater force and power outcomes, better aligning with previously collected measures.

CONCLUSIONS

The present study highlights the proof of concept that a wheel-mounted IMU combined with wheelchair-specific FV modelling provided estimates of force and power that better account for the resistive forces encountered by wheelchair rugby athletes.

Effects of a six-week multimodal training programme on the sprinting ability of adolescent rugby sevens players

This study evaluated the effects of 6-week multimodal training on the sprinting performance and biomechanics of adolescent rugby players. Twenty-four players were assigned to control group (CG) or intervention group (IG). For 6 weeks, CG maintained their training routine, while IG completed a training programme consisting of unresisted sprints, as well as heavy-resisted sprints, running technique drills and lumbopelvic stability. Before and after, sprint performance, horizontal force-velocity profile (FV-h), sprinting kinematics and spatiotemporal data were obtained. After the training, IG reduced the 0-5 m (p = 0.044), 0-10 m (p = 0.046) and 25-30 m (p = 0.035) split times compared with CG. In FV-h, IG displayed a higher maximal theoretical horizontal force (p = 0.035) and ratio of force (p = 0.048) than CG. Regarding kinematic and spatiotemporal variables, only IG improved step length (p < 0.001), step rate (p = 0.005) and distance between knees (p = 0.048) compared with baseline, but there were no between-group differences. Six weeks of multimodal training improved sprinting acceleration and mechanical variables of force application during sprinting of adolescent rugby players. Although IG improved some biomechanical variables compared with baseline, these changes were similar to those observed in CG.

Force-Velocity Profiling in Club-Based Field Hockey Players: Analyzing the Relationships between Mechanical Characteristics, Sex, and Positional Demands

The purpose of this study was to investigate differences between sex and positional demands in club-based field hockey players by analyzing vertical force-velocity characteristics. Thirty-three club-based field hockey athletes (16 males - age: 24.8 ± 7.3yrs, body mass: 76.8 ± 8.2kg, height: 1.79 ± 0.05m; 17 females - age: 22.3 ± 4.2yrs, body mass: 65.2 ± 7.6kg, height: 1.66 ± 0.05m) were classified into two key positional groups (attacker or defender) based on dominant field position during gameplay. Force-velocity (F-v) profiles were established by performing countermovement jumps (CMJ) using a three-point loading protocol ranging from body mass (i.e., zero external mass, 0%) to loads corresponding to 25% and 50% of their own body mass. Across all loads, between-trial reliability of F-v and CMJ variables was determined by intraclass correlation coefficients (ICCs) and coefficient of variation (CV) and deemed to be acceptable (ICC: 0.87-0.95, CV% 2.8-8.2). Analysis by sex identified male athletes had significantly greater differences in all F-v variables (12.81-40.58%, p ≤ 0.001, ES = 1.10-3.19), a more enhanced F-v profile (i.e., greater theoretical maximal force, velocity, and power values), plus overall stronger correlations between relative maximal power (P_MAX) and jump height (r = 0.67, p ≤ 0.06) when compared to female athletes (-0.71≤ r ≥ 0.60, p = 0.08). Male attackers demonstrated a more 'velocity-oriented' F-v profile compared to defenders due to significant mean differences in theoretical maximal velocity (v₀) (6.64%, p ≤ 0.05, ES: 1.11), however differences in absolute and relative theoretical force (F₀) (15.43%, p ≤ 0.01, ES = 1.39) led to female attackers displaying a more 'force-oriented' profile in comparison to defenders. The observed mechanical differences identify the underpinning characteristics of position specific expression of P_MAX should be reflected in training programmes. Therefore, our findings suggest F-v profiling is acceptable to differentiate between sex and positional demands in club-based field hockey players. Furthermore, it is recommended field hockey players explore a range of loads and exercises across the F-v continuum through on-field and gym-based field hockey strength and conditioning practices to account for sex and positional mechanical differences.

The effect of a combined sprint training intervention on sprint force-velocity characteristics in junior Australian football players

Background

Sprint performance in junior Australian football (AF) players has been shown to be a differentiating quality in ability level therefore developing sprint characteristics via sprint-specific training methods is an important aspect of their physical development. Assisted sprint training is one training method used to enhance sprint performance yet limited information exists on its effect on sprint force-velocity characteristics. Therefore, the main aim of this study was to determine the influence of a combined sprint training intervention using assisted and maximal sprint training methods on mechanical characteristics and sprint performance in junior Australian football players.

Methods

Upon completing familiarization and pre-testing, twenty-two male junior Australian football (AF) players (age 14.4 ± 0.3 years, body mass 58.5 ± 10.0 kg, and height 1.74 ± 0.08 m) were divided into a combined sprint training (CST) group (n = 14), and a maximal sprint training (MST) group (n = 8) based on initial sprint performance over 20-meters. Sprint performance was assessed during maximal 20-meter sprint efforts via a radar gun (36 Hz), with velocity-time data used to derive force-velocity characteristics and split times. All subjects then completed a 7-week in-season training intervention consisting of maximal sprinting (MST & CST groups) and assisted sprinting (CST only), along with their usual football specific exercises.

Results

Moderate to large pre-post within group effects (-0.65 ≤ ES ≥ 0.82. p ≤ 0.01) in the CST group for relative theoretical maximal force (F₀) and power (P_max) were reflected in improved sprint performance from 0-20 m, thereby creating a more force-oriented F-v profile. The MST group displayed statistically significant pre-post differences in sprint performance between 10-20 m only (ES = 0.18, p = 0.04). Moderate to high relative reliability was achieved across all sprint variables (ICC = 0.65-0.91), except for the force-velocity slope (S_FV) and decrement in ratio of forces (D_RF) which reported poor reliability (ICC = 0.41-0.44), while the CST group exceeded the pre-post minimal detectable change (MDC) in most sprint variables suggesting a 'true change' in performance across the intervention.

Conclusion

It is concluded that implementing a short-term, combined sprint training intervention consisting of assisted and maximal sprint training methods may enhance sprint mechanical characteristics and sprint performance to 20-meters in junior AF players.

Relevance of force-velocity and change of direction assessments for the ranking position in elite junior tennis players

Purpose

This study aimed to correlate sprint mechanical parameters (SMP) of a linear sprint (LS) and a tennis specific modified 505 (Tm505) change of direction (CoD) test obtained with a motorized resistance device (MRD) to the current tennis ranking position (RP).

Methods

107 male and 86 female elite junior tennis players nationally ranked in the German Tennis Federation between 10 and 18 years participated in the study. According to their age at peak height velocity (PHV), players were divided into pre-PHV, circa-PHV, and post-PHV groups. SMP were derived from instantaneous time-velocity data of two 20 m all-out LS measured with 333 Hz. Further, mean values from two Tm505 trials with constant 3 kg loading over acceleration-deceleration (1a) and reacceleration (1b) phases were measured with an MRD. SMP of LS and CoD measurements were partially correlated with the current RP in the overall national ranking by controlling for biological maturation.

Results

Low to moderate correlations (r_s  = -0.1 to -0.3) were found between SMP and the RP in all male and female age groups. Correlations of the CoD measurements were overall more pronounced, particularly in girls (r_s  = -0.44). All linear SMP, like maximal theoretical force (F₀; N/kg), and maximal theoretical velocity (v₀; m/s), maximal power (P_max; W/kg), improved over maturation for both genders with P_max being most important for sprint performance. Further, P_max was shown to correlate with the girls ranking position (r_s  = -0.31). During the Tm505, matured players achieved significantly faster overall total and CoD times. Positioning of CoM before CoD enlarged over maturation and was found to correlate to the RP in both sexes. In addition, nearly all SMP significantly correlated to the primary performance outcomes in the Tm505 test in both genders (r = -0.3 to -0.6).

Conclusion

CoD performance has a moderate and higher impact on tennis performance compared to LS. CoD performance as well as P_max achieved a higher relevance for the ranking position predominantly in girls compared to boys. Hence, particularly P_max as well as the transfer to on-court CoD motor skills should be a central training goal in elite junior tennis players besides technical skills and should depend on maturation status and gender.

Changes in the Mechanical Properties of the Horizontal Force-Velocity Profile during a Repeated Sprint Test in Professional Soccer Players

The objective was to analyze the changes in the horizontal force-velocity profile (HFVP) during the execution of repeated sprinting. Methods: Seventeen first-division Chilean soccer players completed a repeated sprint protocol consisting of eight sprints of 30 m with 25-s pauses between repetitions. The behavior of HFVP variables in each attempt was recorded from video recordings and analysis in the MySprint® application. Results: Differences (p < 0.05) were found between sprints in the following: time (T), starting from sprint 5 (F = 35.6; η2p = 0.69); theoretical maximum speed (V0), starting from sprint 4 (F = 29.3; η2p = 0.51); maximum power (PM), starting from sprint 5 (F = 17; η2p = 0.52); rate of decrease in force index produced at each step (DRF), starting from sprint 1 (F = 3.20; η2p = 0.17); and RF10, starting from sprint 1 (F = 15.5; η2p = 0.49). In comparison, F0 and RFpeak did not present any differences (p > 0.05). Conclusion: The HFVP variables more sensitive to the effects of fatigue induced by an RSA protocol are those associated with the production of force at high speeds, being V0, DRF, and Pmax, while those that contribute to the generation of force at the beginning of the sprint, F0 and RFpeak, do not present essential variations.

Exploratory Analysis of Sprint Force-Velocity Characteristics, Kinematics and Performance across a Periodized Training Year: A Case Study of Two National Level Sprint Athletes

Objective: This case study aimed to explore changes to sprint force-velocity characteristics across a periodized training year (45 weeks) and the influence on sprint kinematics and performance in national level 100-meter athletes. Force-velocity characteristics have been shown to differentiate between performance levels in sprint athletes, yet limited information exists describing how characteristics change across a season and impact sprint performance, therefore warranting further research. Methods: Two male national level 100-meter athletes (Athlete 1: 22 years, 1.83 m, 81.1 kg, 100 m time: 10.47 s; Athlete 2: 19 years, 1.82 cm, 75.3 kg, 100 m time: 10.81 s) completed 12 and 11 force-velocity assessments, respectively, using electronic timing gates. Sprint mechanical characteristics were derived from 30-meter maximal sprint efforts using split times (i.e., 0-10 m, 0-20 m, 0-30 m) whereas step kinematics were established from 100-meter competition performance using video analysis. Results: Between the preparation (PREP) and competition (COMP) phase, Athlete 1 showed significantly large within-athlete effects for relative maximal power (P_MAX), theoretical maximal velocity (v₀), maximum ratio of force (RF_MAX), maximal velocity (V_MAX), and split time from 0 to 20 m and 0 to 30 m (-1.70 ≤ ES ≥ 1.92, p ≤ 0.05). Athlete 2 reported significant differences with large effects for relative maximal force (F₀) and RF_MAX only (ES: ≤ -1.46, p ≤ 0.04). In the PREP phase, both athletes reported almost perfect correlations between F₀, P_MAX and 0-20 m (r = -0.99, p ≤ 0.01), however in the COMP phase, the relationships between mechanical characteristics and split times were more individual. Competition performance in the 100-meter sprint (10.64 ± 0.24 s) showed a greater reliance on step length (r ≥ -0.72, p ≤ 0.001) than step frequency to achieve faster performances. The minimal detectable change (%) across mechanical variables ranged from 1.3 to 10.0% while spatio-temporal variables were much lower, from 0.94 to 1.48%, with Athlete 1 showing a higher 'true change' in performance across the season compared to Athlete 2. Conclusions: The estimated sprint force-velocity data collected across a training year may provide insight to practitioners about the underpinning mechanical characteristics which affect sprint performance during specific phases of training, plus how a periodized training design may enhance sprint force-velocity characteristics and performance outcomes.

The influence of short sprint performance, acceleration, and deceleration mechanical properties on change of direction ability in soccer players-A cross-sectional study

The study investigated the relationship between short sprint performance and mechanical parameters obtained during the acceleration and deceleration tasks with the change of direction (COD) performance in female and male soccer players. The acceleration and deceleration ability were compared in the "High/Fast" versus "Low/Slow" COD performance group based on a median split analysis in each sex group. One hundred three French soccer players were assessed for the sprinting Force-Velocity (F-V) profile (i.e., theoretical maximal force [F0], velocity [V0], power [Pmax]), 10 m performance, linear deceleration test (maximal braking force [HBFmax], braking power [BPmax], deceleration [Decmax]), and COD performance using 505-test. The 10 m performance was strongly associated with 505-test performance (ES = [0.64 to 0.71]), whereas the sprinting F-V profiles parameters were weakly to moderately correlated with 505- performance (ES = [-0.47 to -0.38]). The BPmax was also moderately associated with 505-test performance (ES: range = [-0.55 to -0.46]). In addition, the High/Fast female COD group presented higher F0, Pmax, HBFmax, and BPmax than the Low/Slow group, whereas the male groups presented very few mechanical differences. Multiple regression analysis shows that the COD performance of male players was determined by 10 m performance and maximum deceleration power. In contrast, no statistically significant model could be found to determine the change of direction performance in female players. In conclusion, the current finding indicated that the only variable strongly associated with COD performance was the linear 10 m sprint time. In the same way, the mechanical parameters obtained from acceleration and deceleration seemed to play a non-neglectable role in this population.